When very long wave guides are disposed in ambient conditions subject to large differences in temperature, as in the case of natural variations in temperature, expansion stresses are produced in the wave guides. This is the case in particular for television transmitters, where the wave guides are made of aluminum and are placed along a steel structure, e.g. a pylon, and where difference in temperature of 50.degree. C. are currently found. For a length of 100 meters, the differential expansion between the wave guides and the steel structure is then sixty millimeters.
A known solution consists in connecting the wave guide to the transmitter by giving it a very large radius of curvature at the foot of the pylon; expansion then affects the radius of curvature without deforming the wave guide too much; in such a solution, free expansion of the wave guide must be allowed for by not fixing it rigidly to the pylon at any point between the foot and the top of the pylon.
Flexible wave guides are also known which allow for differences in expansion; these wave guides are generally of small cross-section. They have relatively high attenuation and they are difficult to manufacture with a large cross-section, as is more particularly required for wave guides for television transmitters.
The invention aims to provide an expansion joint which accommodates the variations in length of a wave guide that is subject to large variations in temperature.
The invention also aims to provide an expansion joint in which the standing wave ratio remains low throughout the whole expansion range.
A further aim of the invention is to seal the expansion joint when the wave guide is pressurised.